Fix chart sizing issue on analytics dashboard

Charts were not rendering properly because admin-script.js targeted a
non-existent canvas ID (peptide-analytics-chart) instead of the actual
IDs (pn-trends-chart, pn-devices-chart, pn-sources-chart). The script
also used hardcoded demo data instead of the peptideNewsDashboardData
object exported from PHP.

Changes:
- Rewrite admin-script.js to initialise all three dashboard charts
  (line, doughnut, bar) using the correct canvas IDs and PHP data
- Set maintainAspectRatio: false so explicit canvas heights are respected
- Add max-height CSS constraint on chart canvases to prevent unbounded
  vertical growth
- Sync JS/CSS to admin/ root directory to match PEPTIDE_NEWS_PLUGIN_URL
  asset path

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

admin/css/admin-style.css

@@ -0,0 +1,139 @@
+/**
+ * Peptide News — Admin Styles
+ *
+ * @since 1.0.0
+ */
+
+/* Dashboard layout */
+.peptide-news-dashboard {
+    max-width: 1400px;
+}
+
+/* Date filter bar */
+.pn-date-filter {
+    display: flex;
+    align-items: center;
+    gap: 10px;
+    margin: 20px 0;
+    padding: 15px 20px;
+    background: #fff;
+    border: 1px solid #e2e8f0;
+    border-radius: 8px;
+}
+
+.pn-date-filter input[type="date"] {
+    padding: 6px 10px;
+    border: 1px solid #cbd5e1;
+    border-radius: 6px;
+}
+
+/* Summary cards */
+.pn-summary-cards {
+    display: grid;
+    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
+    gap: 16px;
+    margin: 20px 0;
+}
+
+.pn-card {
+    background: #fff;
+    border: 1px solid #e2e8f0;
+    border-radius: 10px;
+    padding: 24px;
+    text-align: center;
+    transition: box-shadow 0.2s ease;
+}
+
+.pn-card:hover {
+    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.08);
+}
+
+.pn-card h3 {
+    font-size: 32px;
+    font-weight: 700;
+    color: #1e293b;
+    margin: 0 0 4px;
+}
+
+.pn-card p {
+    font-size: 13px;
+    color: #64748b;
+    margin: 0;
+    text-transform: uppercase;
+    letter-spacing: 0.5px;
+}
+
+/* Charts */
+.pn-charts-row {
+    display: grid;
+    grid-template-columns: 1fr 1fr;
+    gap: 20px;
+    margin: 20px 0;
+}
+
+.pn-chart-wide {
+    grid-column: 1 / -1;
+}
+
+.pn-chart-box {
+    background: #fff;
+    border: 1px solid #e2e8f0;
+    border-radius: 10px;
+    padding: 20px;
+    position: relative;
+}
+
+.pn-chart-box canvas {
+    max-height: 300px;
+    width: 100% !important;
+}
+
+.pn-chart-box h2 {
+    font-size: 16px;
+    font-weight: 600;
+    color: #334155;
+    margin: 0 0 16px;
+    padding: 0;
+}
+
+/* Tables */
+.pn-table-section {
+    margin: 30px 0;
+    background: #fff;
+    border: 1px solid #e2e8f0;
+    border-radius: 10px;
+    padding: 20px;
+}
+
+.pn-table-section h2 {
+    font-size: 16px;
+    font-weight: 600;
+    color: #334155;
+    margin: 0 0 16px;
+}
+
+.pn-table-section .wp-list-table {
+    border: none;
+}
+
+/* Articles page title count */
+.title-count {
+    font-weight: 400;
+    color: #64748b;
+    font-size: 16px;
+}
+
+/* Responsive */
+@media (max-width: 782px) {
+    .pn-charts-row {
+        grid-template-columns: 1fr;
+    }
+
+    .pn-summary-cards {
+        grid-template-columns: repeat(2, 1fr);
+    }
+
+    .pn-date-filter {
+        flex-wrap: wrap;
+    }
+}